Gravitational waves from extreme mass ratio inspirals:challenges in mapping the spacetime of massive, compact objects

Abstract

In its final year of inspiral, a stellar mass (1-10 M⊙) body orbitsa massive (105-107 M⊙) compact object about 105 times,spiralling from several Schwarzschild radii to the last stable orbit. Theseorbits are deep in the massive object's strong field, so the gravitationalwaves that they produce probe the strong-field nature of the object'sspacetime. Measuring these waves can, in principle, be used to `map' thisspacetime, allowing observers to test whether the object is a black holeor something more exotic. Such measurements will require a goodtheoretical understanding of wave generation during inspiral. In thispaper, I discuss the major theoretical challenges standing in the way ofbuilding such maps from gravitational-wave observations, as well asrecent progress in producing extreme mass ratio inspirals and waveforms.